1. Field of the Invention
The present invention relates to a method of manufacturing SiC fiber for reinforcement of SiC composite useful as structural members or parts of a power generating plants, aircraft, spacecraft machine, nuclear reactors, nuclear fusion reactors or the like driven under extremely severe conditions with heavy thermal duty.
2. Description of the Related Art
Various ceramics such as SiC and Si3N4 good of heat-resistance, corrosion-resistance and mechanical strength have been developed so far for structural members or parts of aircraft, spacecraft, nuclear reactors or the like driven under extremely severe conditions. Such ceramics are also used as parts of heat exchangers or mechanical seals driven with heavy duty.
Especially, SiC is a suitable material in various industrial fields from aerospace to nuclear power generation, due to its excellent resistance to heat, abrasion and corrosion as well as chemical stability. SiC is brittle itself, despite of good high-temperature property with a sublimation temperature higher than 2600° C. In order to overcome poor toughness, there are reports on reinforcement of SiC composite with SiC fibers, and various processes such as hot-press and liquid-phase sintering have been proposed for manufacturing SiC fiber-reinforced SiC-matrix composite.
SiC fiber for reinforcement of SiC composite has been prepared from polycarbosilane by a melt-spinning process capable of producing flexible fiber with ease compared with CVD process. The melt-spinning process relies on spinnability and formability of polycarbosilane as a pyrolyzed product of polysilane to a great extent, and enables formation of uniform fine structure free from any fluctuations originated in deviation of a Si/C ratio by baking. Uniformity of the fine structure means that there are no inhibitors against crystal growth and crack propagation. In the uniform structure derived from polycarbosilane, further improvement on physical property, especially heat-resistance of the fiber itself, however, cannot be expected any more.
Spinnability and high-temperature stability of polycarbosilane can be controlled by addition of a metal alkoxide or the like as a spinning aid. A representative metal alkoxide is poly-titano-carbosilane. However, generation of fine structure is derived from precipitation of a secondary phase at a high temperature, so that the fine structure substantially varies in response to a heating temperature and an atmosphere for heat-treatment in addition to presence of a metal alkoxide.
Coarsening of fine structure means fluidization of various grain boundaries in SiC fiber, and causes decrease of heat-resistance, resulting in poor quality reliability of SiC composite. Furthermore, inclusion of foreign elements other than C and Si from a spinning aid accelerates generation of a secondary phase at grain boundaries and put harmful influences on properties of SiC fiber.